rebase without trunk

[skarim]

Add a --no-trunk flag to gh stack rebase that performs only the inter-branch cascade rebase without fetching from the remote or rebasing with the trunk branch.

This is useful when you want to align stack branches with each other (branch 2 onto branch 1, branch 3 onto branch 2, etc.) without pulling upstream changes or rebasing branch 1 onto trunk. Common use case: you've made changes on a lower branch and just want to cascade those changes up through the stack without touching the network or trunk.

Behavior

When --no-trunk is passed:

1. Skips all remote/trunk operations — pickRemote, git fetch, ensureLocalTrunk, fastForwardTrunk, and fastForwardBranches are all gated behind !opts.noTrunk. No network calls are made.
2. Starts the cascade from index 1 — the first branch (index 0) is never rebased onto trunk. The cascade begins with branch 2 rebased onto branch 1, branch 3 onto branch 2, etc.
3. Combines with existing flags — --no-trunk --upstack and --no-trunk --downstack work as expected. startIdx is clamped to max(startIdx, 1) so the trunk rebase is always skipped regardless of other range flags.
4. Single-branch edge case — if the stack has only one branch, --no-trunk results in "No branches to rebase" since the only operation would have been rebasing onto trunk.

Changes

cmd/rebase.go:

• rebaseOptions: Add noTrunk bool field
• rebaseState: Add NoTrunk bool with json:"noTrunk,omitempty" — persisted on conflict so --continue can produce accurate success messages
• RebaseCmd: Add --no-trunk flag definition, update Long description and Example block
• runRebase: Wrap the fetch/trunk/fast-forward block in if !opts.noTrunk { ... }. After computing startIdx/endIdx from --downstack/--upstack, apply if opts.noTrunk && startIdx < 1 { startIdx = 1 }. Save opts.noTrunk into rebaseState on conflict. Update success message to say "without trunk" when in no-trunk mode.
• continueRebase: Read state.NoTrunk and adjust the success message accordingly

cmd/rebase_test.go:

• TestRebase_NoTrunk_SkipsTrunkRebase: Stack [b1, b2, b3] with --no-trunk — verifies only 2 rebase calls (b2→b1, b3→b2), no trunk rebase. Asserts output contains "without trunk".
• TestRebase_NoTrunk_SkipsFetch: Verifies FetchFn is never called when --no-trunk is set.
• TestRebase_NoTrunk_SingleBranch: Single-branch stack with --no-trunk — verifies "No branches to rebase" output.
• TestRebase_NoTrunk_WithUpstack: --no-trunk --upstack from b2 — verifies the combination works correctly (upstack already starts at index 1, so --no-trunk is a no-op for the range).
• TestRebase_NoTrunk_ConflictSavesState: Conflict on b2 with --no-trunk — verifies NoTrunk: true is persisted in the saved rebase state JSON.

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[Copilot]

Pull request overview

This PR adds a --no-trunk flag to gh stack rebase that performs only the inter-branch cascade rebase (branch 2 onto branch 1, branch 3 onto branch 2, etc.) without fetching from the remote or rebasing the first branch onto trunk. This is useful when changes on a lower branch need to be cascaded upward without involving the network or trunk.

Changes:

• Gates all remote/trunk operations (pickRemote, git fetch, ensureLocalTrunk, fastForwardTrunk, fastForwardBranches) behind !opts.noTrunk, clamps startIdx to skip index 0, persists the flag in rebase state for --continue, and adjusts success messages.
• Adds five new tests covering: skip trunk rebase, skip fetch, single-branch edge case, combination with --upstack, and conflict state persistence.
• Updates documentation (README, SKILL.md, CLI reference, workflows guide) with the new flag description and examples.

Show a summary per file

File	Description
cmd/rebase.go	Core implementation: new noTrunk option/state field, conditional remote/trunk block, startIdx clamping, state persistence, adjusted messages
cmd/rebase_test.go	Five new test cases covering --no-trunk behavior and edge cases
README.md	Documents --no-trunk flag in the rebase flags table and examples
docs/src/content/docs/reference/cli.md	Documents --no-trunk flag in CLI reference
docs/src/content/docs/guides/workflows.md	Adds --no-trunk usage example to workflows guide
skills/gh-stack/SKILL.md	Updates skill version, adds --no-trunk to command table, docs, and examples

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[ktravers]

Sounds like something we'll want in the web client too 👀